I created an STL model in 3DSmax, shelled it in meshlab, repaired it in netfabb, and uploaded it to Shapeways. The dimensions of the object appeared constant (about 5cm tall) throughout the process, but after the upload/verification by Shapeways, the dimensions changed considerably.

For reference, here are the actual dimensions reported by the various apps (all on the same STL file):

The Meshlab measuring tool confirmed it's about 5 cm tall as well. Everyone but Shapeways seems to agree with that. What's going on here and, more importantly, how tall with my model actually be when printed?

Is it possible that somewhere along the line, that metric to imperial or vice-versa conversions have been made or that the wrong units have be selected at upload?
This would not account for the differences in dimensions though, however if your model was uploaded as mm and it contains some very small shells, it is possible that those small shells would be removed.

It is also possible that Shapeways Mesh MEdic has 'repaired' your model and by doing so has changed the geometry - one way to check against this is to use NetFabb's Cloud Service which performs pretty much the same repair functions as Mesh Medic with the added bonus of merging mulitple shells into one closed mesh shell. Though again this doesn't seem like there should be an issue as you've used all the right tools for the job.

I can take a look at the model file for you if needs be to see if I can spot anything that could cause the dimensional issues.

I can't find anything that would cause this issue. I'm getting the same as you for dimensions locally no matter what the filetype or software I check the model in, however after uploading to Shapeways, even with different filetypes, the results are the same as yours.

Note that the volume is the same in all your examples, so your model is unlikely to come out distorted. I would guess that there is a difference in how the ShapeWays software calculates the hight over the pointy bit at the top of your model.

I've uploaded JL06, which went directly from MAX through Netfabb and then to Shapeways. The model is shortened after the Shapeways upload AND the volume is reported as 4.64 cm³ instead of the 5.56 netfabb showed.

At least it costs less

I've ordered a print so we'll see if it comes out the correct size or not. This project is a test of the feasibiliy of using Shapeways to produce my product line, so at least it will answer that question one way or the other.

I just ran an experiment, Tilted a basic cube at weird angles. Exported it as a stl, imported it into nettfabb. Everything was ok, till I exported it as a stl, imported into blender. Now the bounding box view was aligned along the xyz axis, which led to weirdness in its dimensions. My guess is that if the model is not properly aligned in its creation, the end result once loaded to shapeways is off kilter in its specs, as long as the volume matchs its good to go.

Have any questions regarding Blender, and need fast answers, you are always welcome at the IRC Server Freenode, channel #blender. As a bonus, several there have experience in modelling for 3D prints.

That's what I thought too Fredd, but the mesh is square to the local and global axis - even finding the outermost vertices and noting their position equates to the dimensions as stated by Ki_Ryn, I even went on a hunt to see if there were any stray vertices not connected to the mesh that could account for the difference is size, but the model is 'perfect'.

I've uploaded JL06, which went directly from MAX through Netfabb and then to Shapeways.
I've ordered a print so we'll see if it comes out the correct size or not. .

The model arrived today and it is the correct length so the error appears to just be in the value displayed by Shapeways. The actual model is not changed (which is good!). This will work for my needs, though I'll have to put a note in the product description about the actual dimensions differing from what is displayed.